The invention concerns a nozzle arrangement in a blow box or any other, equivalent blow member in a paper making machine, comprising one or more nozzles placed in connection with a blow box or pipe, or equivalent member through which nozzles the blowing of air can be applied to a moving member in a paper machine placed in proximity to the nozzles, such as a wire, drying cylinder, guide roll, felt, or the equivalent, and which blow box and its nozzles are arranged at a certain operational safety distance from the moving member.
In the prior art, the multi-cylinder dryers of paper machines in common use consist of two lines of cylinders placed one above the other, in which connection an upper wire or felt as well as a lower wire or felt are used, which wires or felts are guided by guide rolls placed in the gaps between the drying cylinders so that these wires or felts press the web against the cylinder face. The web runs from one line of cylinders to the other in a series of free draws. Inside the multi-cylinder dryer, these free draws of the web, respective faces of the cylinders, and the wires or felts guided by the guide rolls define pockets, which are open at their ends but otherwise closed, the ventilation of these pockets being an important factor with a view to achieving uniformity of drying efficiency and drying results in a multi-cylinder dryer.
In recent years, the running speeds of paper machines have been increasing, and this has had the consequence that these free draws of the paper web have been made shorter particularly in order to reduce the risk of web breaks resulting from fluttering. However, it follows that the above-mentioned ventilation of the pockets has become more difficult, because the size of the pockets has become smaller. Moreover, constantly increasing requirements are imposed for the ventilation of the pockets, because the dwell times of the web in direct connection with the pockets have also become shorter.
In the prior art, a number of different blow devices are known, by whose means air is blown through the felts or wires into the pockets or to other objects.
When disturbances in operation occur, paper waste is produced in paper making machines, which waste frequently forms clods which cause problems in congested locations in the machine, e.g. in the narrow gaps between the blow boxes and wires, drying cylinders or guide rolls. This is why relatively large safety distances are required between the wires or the web and the blow boxes in order that these clods can pass between the blow boxes and the above-mentioned parts without causing damage to their structures. These safety distances are generally in the order of 50 to 100 mm.
Since the air nozzles of the blow boxes must be placed at the aforementioned safety distance, e.g., from a wire, frequently the desired effects of the blowings are not completely achieved, because, for example, the blowing cannot be directed precisely at its target and sufficiently high pressure cannot be achieved by means of the blowings. A typical example of devices wherein drawbacks of the sort discussed above are present are the pocket ventilation pipes described in the Applicant's FI Patent No. 68,278 (corresp. U.S. Pat. No. 4,539,762), which pipes, placed at a distance of, e.g., 100 mm from the wire, do not produce a sufficiently large quantity of air passing through the wire to ensure adequate pocket ventilation.